I have the 17-40L and the Tamron 24-70 (bought last week).
I was using the 17-40 as a walkaround, but now, personally, if 24mm is wide enough, I can't see a reason to get any zoom in this range other than the Tamron. I've been very happily surprised with just how sharp and contrasty it is. It gets close to the 70-200 f2.8 II (not quite as sharp but good enough for me not to worry too much which I use at 70mm). Feels really solidly put together too.
On a tripod, stopped down to f8 or more, the 17-40 is great, but the Tamron is sharper with better contrast and clarity wider open, has better corners, has really good VC and opens to 2.8 of course. Build seems at least as good. I wont be using the 17-40 anymore except on the rare occasions I need UWA. The Tamron does have a little more distortion at 24mm, but DXO (or I would assume Lightroom) corrects this automatically and I have not found it an issue so far.
I have not used the 24-105L much but a friend has it and somehow her shots seem slightly more 'muddy' (less sharp, lower contrast, images don't quite pop the same somehow) - both using the 5D3. Not saying it's a bad lens, but it did not excite me particularly, and f2.8 swung it for me.
Tripod, small apertures and UWA get the Canon.
Anything else, I can recommend the Tamron. I think I'm going to turn into a Tamron fanboy pretty quickly!